Raw material for cellulose derivatives and process of preparation



Patented Oct. 1, 1929 UNITED STATES PATENT OFFICE GEORGE A. RICHTER AND MILTON O. SCHUR, F BERLIN, NEW HAMPSHIRE, AS-

SIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE RAW MATERIAL FOR CELLULOSE DERIVATIVES AND PROCESS OF PREPARATION No Drawing.

In manufacturing cellulose derivatives of high purity and stability, it is essential that the cellulose employed as a raw material for the derivatives be of high purity and stability,

as otherwise impurities are converted along with the cellulose, this not only consuming additional chemical, but also resulting in reaction products which color and render the derivative unstable. High grade cotton, being a substantially pure form of alpha cellulose, has usually been employed for the production of the highest grade derivatives. Less expensive raw materlals, such as Wood pulp, even when refined to high alpha cellulose content, have not heretofore yielded derivatives of a quality equal to those pre pared from cotton, unless special measures are taken to remove from the pulp certain impurities which survive the usual refining treatment to a very slight but positive extent and which exert a powerful and highly undesirable coloring effect in the preparation of cellulose derivatives.

If wood pulp is closely examined, it will be observed that it consists of fiber units of random sizes. Hence, while it is common to designate pulp by a certain average fiber length, the individual fibers deviate widely from this average, some being considerably above and some considerably below. A considerable proportion of the pulp below average fiber length consists of fibrillae, short and broken fibers, and colloidal cellulose. Cellulose in such finely divided condition and hereinafter designated fines is character ized by its high adsorptive properties. Hence it is not surprising that most of the impuri ties in the pulp, particularly specks and resinous materials including resins, gums, waxes and fats, are adsorbed by and associated with the fines of the pulp, in some cases the fines of an unbleached pulp containing over 7% of substance soluble in hot carbon tetrachloride or other organic solvent. The ash content of the fines is also high, and this fraction of the stock is so sensitive to heat that, when made into a sheet and dried on a steam drum under conditions simulating pulp and paper mill practice, a distinct yellowing takes place. While the percentage and composition- Application filed August 5, 1927. Serial No. 210,998.

of the fines in pulp depend upon the severity I and nature of the fiber-liberating process and upon the character of the original wood, nevertheless the fines are always darker in color and more resistant to whitening than the rest of the pulp, and yield derivatives dark in color and comparatively unstable. In application, Serial No. 207,314, filed July 20, 1927, by Milton 0. Schur and Robert A. Webber, a process is disclosed comprising the separation of the fines from pulp before it is converted into derivatives. Such a process is particularly advantageous in the case of pulp refined to high alpha cellulose content, for a refined pulp free from fines yields derivatives substantially as good as those producible from cotton. The process disclosed in that application, however, yields a considerable quantity of fines as one of its products. Owing to their short fiber length and the impurities carried thereby, the fines are of low value, being suitable as a raw material for the manufacture of comparatively cheap apers or derivatives where color and sta-.

ility are characteristics of secondary importance, low price being more important.

In accordance with the process of the present invention, the fines are deresinified and cleansed to a purity and stability substantially equal to the pulp from'which their separation was effected. This is accomplished by digesting the fines in a saponaceous reagent which serves to disperse or colloidally dissolve the adsorbed impurities and then washing the reagent therefrom. A process such as described is especially advantageous, as the product not only is in a condition far more suitable for use as a-papermaking raw material, but is in a physical condition very favorable for conversion into derivatives. Thus, owing to its finely divided condition, it reacts readily with chemicals to produce derivatives. In the viscose-rayon process, for instance, after treatment with caustic soda solution, the period of ageing to effect depolymerization may be shortened and at the same time a thoroughly depolymerized product which xanthates quite readily and completely, obtained.

The separation of the fines from the pulp 'may be effected before or after the pulp has been subjected to chemical processing intended to refine it for conversion into derivatives. A specific example of procedure ma be substantially as follows. The unbleac ed pulp is treated with chlorine water, then digested in an alkaline liquor, and finally bleached, this series of chemical treatments serving to refine the pulp to high alpha cellulose content and whiteness. separated from the pulp. This may be ac complished by Washmg the pulp as a thin layer on fine mesh wire, for instance, 50-mesh Fourdrinier wire, or on thin plate having fine perforations of, say, 0.02 inch in diameter. Or such washing may be efiected by repeatedly diluting the pulp with fresh filtered water,

and then flowing and thickening the pulp a inst the screenin or perforated plate w ile in an incline position. The fines present in the wash water may be recovered on a thickener or by other suitable means. In lieu of separating the fines, the long fibers may be separated from the pulp by passing edgeresenting members through the pulp and t en washing and recovering the long fibers from the members, as described in application Serial No. 206,477, filed July 18, 1927, by liobert A. Webber, leaving the fines in the residual pulp.

The fines thus separated and containing most of the impurities are digested in a soap solution containing about 023% soap. If desired, peptizing agents such assodium phos phate or borax may be added to the solution to increase the dispersing activity of the solution. Digest-ioh efi'ects a dispersion or fixation of insoluble soaps on the cellulose.

colloidal solution of the resin and specks associated with the fines, so that the digested product is as free from these impurities as the long fiber separated therefrom, contain- .ing less than 0.1% of resinous impurities.

The digested product is washed free of soap solution containing the removed impurities,

and is preferably finally subjected to light bleaching to producea snow-white product. This product is eminently suitable for the manufacture of derivatives.

If the fines have been separated from the unbleached or. unrefined pulp, they may be independently refined to high alpha cellulose content. Thus, they may first be chlorinated,

then, alkaline-digested, and finally bleached tolhighwhiteness. During alkaline digesemployed in lieu of the usualcalcium base bleach, in order to avoid the precipitation and Even if the pulp as a whole has been treated with soa solution as described in our application, erialiNo. 202,4;54, filed July 29, 1927, so that its resin content has been reduced to The fines may then be maaeae less than 0.1%, if a separation of the fines from the pulp has subsequently been efiected, it may be advantageous to treat these fines again with soapsolution, as their resin content may be considerably'in excess of 0.1%. Such treatment, followed by a subsequent light bleaching, results in a snow-white product which,-because"of-its higher activity, may be even-more suitable than a long-fiber raw material.

Having thus described certain embodiments of this invention, it is obvious to those skilled in the art that change and modification-might be made therein without departin from the spirit or scope of invention as de 'ned in the appended claims.

What we claim is: 1

1. A process which comprises removing fine, short and broken fiber from pulp, and deresinifying and cleansing the removed material.

2. A process which comprises removing fine, short and broken fiber from pulp, and digesting the removed material in a saponaceous reagent.

ceous reagent, and converting the digested product into a derivative.

4. A process which com rises removing fine, short and broken fiber trom wood pulp, digesting the removed material in a. saponaceous reagent, and bleaching the digested product.

5. A process which com rises removing fine, short and broken fiber rom wood pulp,

and digesting the removed material in a saponaceous reagent containing a peptizing agent.

content, digesting the removed material in. a saponaceous reagent, bleaching the digested product, and converting the bleached product into a cellulose derivative.

7. A product consisting of fine, short and broken cellulose fiber having a resin content of less than 0.1% and convertible intoderivatives of a quality substantially equal to those .producible' from high grade cotton.

8. A product consisting of fine, short and broken wood fiber having a snow-white color and a resin content of less than 0.1%.

9. A product consisting of fine, short and broken fiber refined tohigh alpha cellulose content, having a snow-white color and a resin content of less than 0.1%.

In testimony whereof we have afiixed our signatures.

GEORGE A. RICHTER. MILTON O. SCHUR'. 

